Horizontally opposed, piston-driven engines are known in the art, and widely used in the aviation industry. However, there is a need in the industry to provide an engine that does not rely on fuel containing tetraethyl lead, a component currently contained in aviation gasoline. There is a further need for an engine offering high specific power output in a light weight package.
In the past, there was a tremendous amount of effort to increase the specific power of engines. In particular, the efforts were focused at delivering light-weight, high-power, piston engines for use in military fighter and bomber airplanes. The direction generally taken by both the Allied and Axis powers was to rely heavily on two particular strategies. The first was to develop air-cooled radial engines. These engines were designed with the shortest crankshaft available (single-throw, master-slave rod), and were arranged to make the best use of the fiontal area to effectively cool the vital engine components, as shown in FIGS. 1 and 2.
Another strategy employed was to use the Vee (or “V”) configuration to reduce weight by minimizing the crankshaft length. A reduction in crankshaft length consequently reduces the engine volume and weight of the engine. Length was so important, that in extreme cases the fork-and-knife method was used to minimize engine cylinder bank offset, and further reduce weight, as shown in FIG. 4. The engines were generally smaller in displacement than the air-cooled counterparts, and were comprised of ideally-balanced inline configurations sharing a common crankshaft. For this reason, the dominant liquid-cooled engine was a V-12 because it was made up of two perfectly balanced six cylinder engines. FIG. 3 is an example of a V-12 engine. The V-12 also had a certain level of redundancy with the ability to pair ancillaries etc.
In the past years Schrick (assignee of the present application) has made some monumental advances with regards to utilizing diesel engines in aero applications. One such engine was the air-cooled Hurricane engine as shown in FIG. 5, which used strategies similar to the large radial, gasoline powered engines in the Second World War. This twin cylinder diesel engine was air-cooled, and shared many of the basic design elements of the Second World War engines with advances in materials and processing applied. The engine was remarkable in that it achieved an installed weight of 1.15 lbs/hp in the 600 cc displacement class for a diesel engine.
Accordingly, there is a need for a more production feasible solution for the General Aviation (hereinafter “GA”) community. Current GA engines have their roots in the air-cooled engines of the Second World War era. They are identical in many respects, with the exception of being horizontally-opposed engines. This engine configuration has been used in the past by Volkswagen and Porsche, as well as the dominant aero engine manufacturers Lycoming and Continental. FIG. 6 is a depiction of this engine type.
Although the engine configuration of FIG. 6 is not ideal from a weight perspective, it does provide the cooling air space necessary for the air-cooled cylinder heads. It also allows for a more streamlined package within the confines of an aircraft installation. However, the horizontally opposed engine is unnecessarily long, due to the nature of its crankshaft layout. In this configuration, each throw of the crankshaft is used for a single cylinder.
There is a further need in the industry for an engine that does not rely on tetraethyl-based lead. Lead additive is currently vital to aviation fuel for its anti-knock properties, however it is very harmful to the environment and only produced today in limited quantities.